Cathode-ray tube scanning system



Get. 31, 1939. M. CAWEIN 2,177,,6

CATHODE-RAY TUBE SCANNING SYSTEM Filed Dec. 24, 11936 FRAME FREQUENCY GENERATOR LINE FREQUENCY GENERATOR ATTORNEY.

Patented Oct. 31', 1939 PATENT OFFICE CATHODE-RAY TUBE SCANNING SYSTEM Madison Cawein, Manhasset, N. Y., assignor to Hazeltlne Corporation, a corporation of Delaware Application December 24, 1936, Serial No. 117,458

3 Claims.

This invention relates to cathode-ray tubes, and more particularly to scanning systems for such tubes.

More specifically, this invention relates to 5 scanning systems for cathode-ray tubes useful in television systems and including signal-generating tubes for television transmitters and signalreproducing tubes for television receivers. A tube of either of these types comprises an elongated evacuated envelope including at one end a plurality of electrodes, commonly referred to as an electron gun, which serve to develop, focus, and accelerate a beam of electrons or cathode ray toward a target which is disposed in the envelope at the opposite end. In a signal-generating tube, the target has a photosensitive surface, and images of the scenes to be transmitted are focused on the target and produce photoelectric effects which vary over the extent of the target in accordance with the light intensity of correspending portions of the images. Proper deflection of the cathode ray to scan the target develops video-frequency modulation voltages in the output circuit of the tube including a connection to the target. On the other hand, in a signalreproducing tube, the target comprises a fluorescent screen which becomes luminous when excited by a cathode ray. The intensity of the cathode ray in the signal-reproducing tube is modulated in accordance with the video-frequency components transmitted and the beam. is deflected to scan the fluorescent screen in the same manner as, and in synchronism with, the scanning of the target of the signal-generating tube, so that the transmitted scene is reconstructed on lhc fluorescent screen.

For effecting the desired scanning of the target by the cathode ray, periodic electric fields, either electrostatic or electromagnetic, are utilized to deflect the ray after it emerges from the electron gun.- Ordinarily, one of the fields deflects the beam in one direction at a relatively high frequency, while the other field deflects the beam in a direction normal to that of the first field at a relatively low frequency, so that series of parallel lines, each series or frame representing the complete scene, are successively scanned on the target. To this end, frame-frequency and line-frequency generators are utilized for develbu oping voltages or currents of a saw-tooth wave form which are impresed upon deflecting plates or passed through deflecting coils, respectively, thereby to develop the required electrostaticor electromagnetic fields. It has been found diffi- 55 cult to develop voltages orcurrents of the proper Wave form having sufficient amplitude for proper scanning, particularly line scanning, which is at extremely high frequencies. Voltages and currents of the required wave forms, but of relatively low amplitude, however, may be developed with 5 relatively simple apparatus and without diificulty.

It is an object of the present invention, therefore, to provide a cathode-ray tube scanning system. which requires scanning voltages or currents 10 of only relatively low amplitudes.

It is a further object of the invention to provide a scanning system of the character described; whereby the aspect ratio of the scanning pattern produced on the target by the scan-- 15 ning coils or plates, per se, may be modified in a predetermined manner.

In accordance with the present invention, there is provided, in combination with a cathode-ray tube including an electron gun and a target, a scanning system which comprises means for pcriodically deflecting the ray to scan the target. Additional means are arranged to produce an invariable electric field having a component normal to the path of the ray, which field so refracts the ray, when deflected, as to modify the aspect ratio of the scanning pattern on the target.

More particularly, in a preferred embodiment of the invention, the cathode-ray tube comprises an elongated envelope including an electron gun at one end and a target at its opposite end, and a deflecting system arranged adjacent the electron gun to provide deflecting fields for causing the ray to scan a rectangular pattern, comprising a series or frame of parallel paths, on the target. The refracting means comprises means, such as one or more permanent magnets, arranged between the deflecting fields and the target to produce an invariable magnetic field. This retracting field has a component normal to a plane through the axis of the tube, that is, normal to a plane through the path of the ray and parallel to one deflecting field, and its intensity is zero along an axial plane normal to the aforesaid plane through the axis and gradually increases linearly and with opposite polarity at either side of this plane. With such an arrangement, the ray is so refracted, when deflected, as to effect an increase in'one dimension of the pat- 5o tern scanned on the target.

In this specification and in the appended claims, the terms deflection and refraction are employed to signify changes in the direction of travel of the cathode ray from the direction erator is preferably designed to develop scanning currents of sufiicient amplitude to provide the required vertical deflection. In view, however, of the relative difficulty mentioned above in obtaining line-frequency deflecting currents of proper wave form and adequate amplitude, the line-frequency generator is preferably designed to provide currents of the proper wave form, but of relatively low amplitude, permitting the use of a line-frequency generator apparatus of relatively simple design. With such an arrangement alone, the deflecting circuits would develop, in a section perpendicular to the axis of the tube, or normal path of the ray, a rectangular scanning pattern having a greater height than width, the outline of which is indicated by the broken lines 21, 28 of Fig. 2. The refracting field provided by magnets 24 and 25, however, serves effectively to increase the deflection of the cathode ray in the horizontal direction and, thus, to modify the scanning pattern to the desired proportions, that is, to increase the ratio of the width to the length of the scanning pattern to increase the aspect ratio, at the section mentioned above, as indicated by the broken lines 21, 29, 30 in Fig. 2, without otherwise altering its configuration. A rectangular scanning pattern of the desired aspect ratio will, therefore, be scanned on the taret.

It is to be noted that the arrangement of the preferred embodiment of the invention, whereby the horizontal deflection is effectively increased, constitutes only one of many possible applications of the present invention. It will be readily appreciated by those skilled in the art that, if desired, deflecting fields may be provided which are of such forms as to develop scanning patterns fective to modify both deflections at both frequencies.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from this invention, and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true scope and spirit of this invention.

What is claimed is:

1. In a cathode-ray tube system including a target and means for developing and focusing a cathode ray, a scanning system comprising means disposed intermediate said ray-focusing means and said target for deflecting the ray in two directions normal to each other to scan parallel paths on the target, and means disposed intermediate said deflecting means and said target for producing an electric field having a component normal to one of said directions and of a uniform gradient of field intensity in said one of said directions for so retracting said ray, when deflected in said one of said directions, as effectively to increase said deflection, so as to alter the ratio of the width to the length of the scanningpattern on said target without substantially otherwise altering its configuration.

2. In a cathode-ray tube system including a target and means for developing and focusing a cathode ray, a scanning system comprising means disposed intermediate said ray-focusing means and said target for deflecting the ray to scan parallel paths on the target, and means disposed intermediate said deflecting means and said target for producing an electric field having a component normal to said paths and of opposite polarities on opposite sides of an axial plane normal to said parallel paths for so retracting said ray, when deflected, as to modify the aspect ratio of the scanning pattern on said target.

3. In a cathode-ray tube system including a target and means for developing and focusing a cathode ray, a scanning system comprising means disposed intermediate said ray-focusing means and said target for deflecting the ray to scan parallel paths on the target, and means disposed intermediate said deflecting means and said target for producing an electric field having a component normal to said paths, of zero intensity at an axial plane normal to said parallel paths, and of uniform gradient of field intensity in the direction of said paths at the opposite sides of said plane for so refracting said ray when deflected as to modify the aspect ratio of the scanning pattern on said target.

MADISON CAWEIN. 

